Biodiesel fuels are mono-alkyl (e.g., methyl) esters of long chain fatty acids derived through saponification of the glycerol triesters of vegetable oils and animal fats. When used “straight,” the biodiesel fuel is referred to as “B100”. When blended into ultra low sulfur diesel (ULSD, having below 15 ppm sulfur content) or other petroleum-based diesel fuels, the blended fuel is named according to its percentage of biodiesel concentration. For example, fuel containing 20% biodiesel is referred to as “B20” and fuel containing 10% biodiesel is referred to as “B10”. Due to possible stability and performance issues, diesel engine operators are in need of an on-site test which can quickly quantify the percentage of biodiesel in fuel stores prior to fueling operations.
On-site testing is important in the biodiesel fuel industry because different customers desire a quantitative analysis of fuels before using the fuels. For example, nuclear power plants desire little to no biodiesel in their diesel fuels. However, the trucking industry does want biodiesel in their ULSD fuels to reduce environmental contaminants. Further complicating the situation, a large number of the nuclear power plants do not use ULSD fuels, but rather still use non-ULSD diesel fuels (such as low sulfur and regular sulfur diesel fuels) having a higher sulfur content (up to 400 ppm sulfur for low sulfur fuel and up to 1500 ppm for regular sulfur diesel fuel), as well as other easily oxidizable compounds, such as phenols, amines, and unsaturated molecules.
Although analytical techniques based on gas chromatography (GC) and Fourier transform infrared (FTIR) spectrophotometry have been used successfully to measure the percentage of biodiesel in ULSD and other non-ULSD diesel fuels, they are not suitable for on-site analyses. Moreover, other compounds present in ULSD, such as carboxylic acids, hydroperoxides, etc., limit the detection capabilities of the GC and FTIR techniques of biodiesel fuel concentrations that are below about 2% of the total fuel. Therefore, there exists a need for a simple, accurate, on-site biodiesel concentration quantification test for blended biodiesel and ULSD or other non-ULSD diesel fuels.